Visual prosthesis fitting

ABSTRACT

Methods and devices for fitting a visual prosthesis are described. In one of the methods, threshold levels and maximum levels for the electrodes of the prosthesis are determined and a map of brightness to electrode stimulation levels is later formed. A fitting system for a visual prosthesis is also discussed, together with a computer-operated system having a graphical user interface showing visual prosthesis diagnostic screens and visual prosthesis configuration screens.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional PatentApplication Ser. No. 60/795,936, filed Apr. 28, 2006 for “VisualProsthesis Fitting” by Avi Caspi, Kelly H. McClure and Robert J.Greenberg, U.S. provisional Patent Application Ser. No. 60/834,239,filed Jul. 28, 2006 for “Visual Prosthesis Configuration and FittingSystem” by Robert J. Greenberg, Matthew J. McMahon, Grant Palmer andKelly H. McClure, U.S. provisional Patent Application Ser. No.60/838,433, filed Aug. 16, 2006 for “Visual Prosthesis Configuration andFitting System” by Robert J. Greenberg, Matthew J. McMahon, Grant Palmerand Kelly H. McClure, U.S. provisional Patent Application Ser. No.60/848,068, filed Sep. 29, 2006 for “Chapter 4: Clinical Fitting &Psychophysical Testing” by Robert J. Greenberg, Kelly H. McClure,Matthew J. McMahon, and Arup Roy, and U.S. provisional PatentApplication Ser. No. 60/834,778, filed Jul. 31, 2006 for “System andMethod for Spatial Mapping of a Visual Prosthesis” by Avi Caspi, MatthewJ. McMahon, and Robert J. Greenberg, the disclosure of all of which isincorporated herein by reference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The present invention was made with support from the United StatesGovernment under Grant number R24EY12893-1, awarded by the NationalInstitutes of Health. The United States Government has certain rights inthe invention.

FIELD

The present disclosure relates to visual prostheses. More particularly,the present disclosure relates to configuring a visual prosthesisimplanted in a patient.

BACKGROUND

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparatuses to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular visual prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases such as retinitis pigmentosaand age related macular degeneration which affect millions of peopleworldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the information as a sequence of electricalpulses which are relayed to the nervous system via the prostheticdevice. In this way, it is possible to provide artificial sensationsincluding vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretial). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, and avoid undue compression of thevisual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal array to the retina. U.S. Pat. No. 5,109,844 tode Juan describes a flat electrode array placed against the retina forvisual stimulation. U.S. Pat. No. 5,935,155 to Humayun describes avisual prosthesis for use with the flat retinal array described in deJuan.

In outer retinal degeneration, such as retinitis pigmentosa (RP), thephotoreceptors and their supporting retinal pigment epithelium areimpaired. In RP (incidence 1:4000) legal blindness is reached after 25years. In many RP patients over sixty years of age, elementary visionwith only gross movement or bright light perception remains, with littleor no appreciable peripheral vision. Eventually, even light perceptionmay recede. Currently, there is no treatment that stops or reverses theloss of photoreceptors in retinitis pigmentosa.

Traditionally, the approach to vision rehabilitation in subjects withretinitis pigmentosa has been to use the remaining vision with opticalaides. If no useful vision is achieved, auditory or tactile informationis substituted (e.g. Braille, cane travel, etc.). Attempts to remedy oralleviate vision loss have been made by replacing damaged cells or byelectrically stimulating an undamaged proximal level, bypassing impairedcells. Replacement of damaged photoreceptors has been studied in animalsthrough transplantation. Although there are indications thattransplanted photoreceptors can make functional connections, manyquestions remain about the optimal methods to achieve long term graftsurvival and functionality in a human eye.

More recently, visual prostheses have been developed to address theextreme low vision population with retinal degeneration. Electricalstimulation at the primary visual cortex has been attempted and has theadvantage of not requiring a viable optic nerve. However, such corticalstimulation has its own risks, such as exposing the brain to surgicalcomplication and infection.

Stimulation at more distal neuronal locations has received recentattention and may provide an alternative in an outer retinaldegenerative disease such as retinitis pigmentosa. Electricalstimulation of the optic nerve has been used to elicit a sensation ofstreaks or dots (phosphenes). Also, electrical stimulation through acontact lens electrode elicits phosphenes in subjects with advancedphotoreceptor degeneration. These perceptual responses, and theelectrically evoked responses recorded from the scalp in response tosuch stimuli, have been interpreted as evidence that inner retinal cellsin subjects with photoreceptor degeneration retain at least partialfunction. However, the phosphenes elicited with a contact lens electrodeor by electrical stimulation of the optic nerve lack well defined shapeor localization.

The production of a small localized visual percept that might allow thegeneration of a two-dimensional array of phosphenes to provide“pixelized visual input” has been explored in both acute and chronicstudies of blind subjects. Even partial restoration of vision insubjects blind from photoreceptor degeneration has been shown to beimportant.

SUMMARY

According to a first aspect, a method for fitting a visual prosthesishaving a plurality of electrodes is disclosed, the method comprising:determining at least one level on a first electrode by patient feedback; determining at least one other level for subsequent electrodesbased on previous results and further patient feedback; and creating andstoring a map of brightness to electrode stimulation levels based on theestablished levels.

According to a second aspect, a method for fitting a visual prosthesishaving a plurality of electrodes is disclosed, comprising: providing avideo camera associated with a pair of glasses; capturing an imagethrough the video camera; sending the image to a video processing unit;converting the image to a digital image; processing the digital image toobtain a processed digital image; and presenting the processed digitalimage to the retina of a subject by way of electrical stimulation.

According to a third aspect, a computer-operated system comprising adisplay component is disclosed, the display component having a graphicaluser interface associated with a method for fitting a visual prosthesishaving a plurality of electrodes, the graphical user interfacecomprising: a visual prosthesis diagnostic screen; and a visualprosthesis configuration screen.

According to a fourth aspect, a method for providing a directmeasurement of individual phosphene locations within a video image isprovided, comprising: stimulating a plurality of electrodes, eachelectrode producing a phosphene when stimulated; asking a subject tolocate the phosphenes; and recording a subject's location of thephosphenes in the video image.

According to a fifth aspect, a device for implementing any one of themethods and/or method steps disclosed in the present specification,drawings or claims, is disclosed.

Further embodiments are shown in the specification, drawings and claimsof the present application.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 show a retinal stimulation system.

FIGS. 3 and 4 show flow charts listing some of the steps of the visualprosthesis fitting method according to the present disclosure.

FIG. 5 shows a current v. brightness diagram of brightness functions.

FIG. 6 shows a flow chart listing some of the steps of the visualprosthesis fitting method according to the present disclosure.

FIGS. 7 and 8 show placements of a subject while performing a visiontest.

FIG. 9 shows flowchart related to vision tests performed on a subject.

FIG. 10 shows components of a fitting system.

FIG. 11 shows a Main Menu computer screen.

FIG. 12 shows a Login computer screen.

FIG. 13 shows an ‘Electrode Integrity’ message box.

FIG. 14 shows a diagnostics computer screen.

FIG. 15 shows a ‘Measuring Impedance’ message box.

FIG. 16 shows a computer screen indicating impedance values.

FIG. 17 shows a message box indicating progress of waveformmeasurements.

FIGS. 18 and 19 show waveform computer screens.

FIG. 20 shows a computer screen with different subsections of a ‘video’application.

FIG. 21 shows a ‘Load’ computer screen.

FIG. 22 shows a ‘stimulation’ computer window.

FIG. 23 shows a ‘waiting for connection’ message box.

FIG. 24 shows a computer window requesting specific information.

FIG. 25 shows a ‘connected’ message box.

FIG. 26 shows a Psychophysical Test System (PTS) main screen.

FIG. 27 shows a ‘Threshold with Method of Adjustment’ screen.

FIG. 28 shows a waveform related to FIG. 29.

FIG. 29 shows a ‘Threshold Test’ computer screen.

FIGS. 30 and 31 show warning dialog message boxes.

FIG. 32 shows a ‘RUNNING: Threshold with method of adjustment’ message.

FIG. 33 shows a ‘Threshold Test with Method of Adjustment’ message box.

FIG. 34 shows an ‘Input Your Comments’ message box.

FIG. 35 shows a ‘Brightness Matching’ computer screen.

FIG. 36 shows an ‘EXPERIMENT: brightness matching’ message box.

FIGS. 37 and 38 show warning dialog message boxes.

FIG. 39 shows a ‘Brightness Matching’ computer screen.

FIG. 40 shows an ‘Input Your Comments’ message box.

FIG. 41 shows a ‘Simple Direct Stimulation’ computer screen.

FIG. 42 shows an ‘EXPERIMENT: direct stimulation’ message box.

FIG. 43 shows a warning dialog box.

FIG. 44 shows an ‘Input Your Comments’ message box.

FIG. 45 shows a side view of the human fovea.

FIG. 46 shows a block diagram of a visual prosthesis.

FIG. 47 shows a system for direct stimulation of electrodes andrecording the spatial location of resulting phosphenes.

FIG. 48 shows a single electrode phosphene map.

FIG. 49 shows a single electrode phosphene location map.

FIG. 50 shows an entire array phosphene location map.

FIG. 51 shows phosphene resulting from simulation of a row and column.

In the following description, like reference numbers are used toidentify like elements. Furthermore, the drawings are intended toillustrate major features of exemplary embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of everyimplementation nor relative dimensions of the depicted elements, and arenot drawn to scale.

DETAILED DESCRIPTION

The present disclosure provides a method of fitting, configuring andoptimizing a visual prosthesis (i.e. device) for an individual patient(i.e. subject) including creating a map of brightness to electricalstimulation levels for each electrode, and using that map for thestimulation of retinal neurons to create artificial vision.

A Retinal Stimulation System, disclosed in U.S. application Ser. No.11/207,644, filed Aug. 19, 2005 for “Flexible Circuit Electrode Array”by Robert J. Greenberg, et, al. incorporated herein by reference, isintended for use in subjects with retinitis pigmentosa. FIG. 1 and FIG.2 show a Retinal Stimulation System 1 wherein a patient/subject isimplanted with a visual prosthesis to be fitted, configured andoptimized according to the present disclosure.

The Retinal Stimulation System 1 is an implantable electronic devicecontaining electrode array 2 that is electrically coupled by a cable 3that pierces sclera of the subject's eye and is electrically coupled toan electronics package 4, external to the sclera. The RetinalStimulation System 1 is designed to to elicit visual percepts in blindsubjects with retinitis pigmentosa.

The fitting system and method according to the present disclosure may beused to establish the most effective Video Processing Unit (VPU)settings for subjects implanted with a visual prosthesis. Thepsychophysical testing according to the present disclosure will be usedto establish the electrical pulse parameters for stimulating retinalneurons and to determine the optimal method for transforming the videoinput signal to a useful pattern of electrical stimulation.

Establishing a stimulation level that is just detectable to a subject(threshold) allows establishing the lowest stimulation value to be usedwhen mapping the darkest part of the video image to a stimulationprofile. A 150-750 ms train of 10-100 Hz pulses (e.g., nine or tenpulses) may be used as the standard stimulus to determine the threshold.The current threshold for each individual electrode may be determinedusing a method of adjustment.

Reference can be made to FIG. 3, which shows steps for performing thevisual prosthesis fitting method according one of the embodiments of thepresent disclosure. The threshold level of a first electrode isinitially determined in S1. The maximum level of the first electrode isthen determined in S2.

Threshold and maximum levels for subsequent electrodes are determined inS3. A map of brightness to electrode stimulation levels based on theestablished thresholds and maximums is created and stored in S4. Asshown in S5, the threshold level of the first electrode can bedetermined through a 250 ms train of nine 40 Hz pulses. As shown in S6and S7, the maximum level on the first electrode can be determined byeither reaching 75% of the chare density safety limit or by reaching themaximum comfort level of the subject. Finally, S8 shows that the maximumlevel can be reached by gradually increasing the amplitude of thestimulation pulses.

Electrode brightness rating measurements will allow to equate thestimulation levels of different electrodes so that they producephosphenes of equal brightness. This is because different electrodeshave different gains, i.e. the relationship between stimulation leveland perceived brightness varies from electrode to electrode. A 250 mstrain of 40 Hz pulses (a train of 9 pulses) may also be used as thestandard stimulus for rating the brightness of each electrode. As alsoshown in step S9 of FIG. 4, one electrode (e.g., the electrode from the32 electrodes in the center of the array that has the median thresholdvalue, see S10 in FIG. 4) may be chosen as the “standard” electrode. Asalready seen from S6 and S8 in FIG. 3, amplitude of the pulses may begradually increased by the experimenter until the standard electrode isat 75% of the safety limit for chronic use. This stepping up is toprevent pain sensation when stimulating the standard electrode.

If the maximum comfort level is reached before the safety limit then theexperimenter should: (i) Choose a different electrode to be the standardelectrode. In this case, the more sensitive electrode that was theinitial standard electrode becomes a test electrode. (ii) If the secondchoice of standard electrode also results in pain when stimulated belowthe safety limit then set a “maximum” limit based on subject's comfortrather than safety limits. In this case the comfort limit is treatedexactly as the safety limit for the process of brightness matching.

Once the amplitude of the standard stimulus has been chosen, thebrightness due to that stimulus will be defined as a “10”. Each of theelectrodes will be stimulated at its maximum chronic level and thesubject will rate the relative brightness, for example, 20 if it istwice as bright as the standard, 5 if it is half as bright. The subjectwill compare the brightness of every electrode with reference to thestandard electrode. Two pulses will be presented, and the subject willsay which stimulus interval seemed brighter. See S11 in FIG. 4. This maybe performed until brightness matched map across all electrodes withreference to the standard electrode.

The procedure for converting a video camera input to a pattern ofelectrical stimulation can be broken down into two general parts: thevideo chain and the electrode map (emap).

The Video Chain

The image is initially captured by a video camera mounted on the frameof the glasses. This video image is sent to a Video Processing Unit(VPU), where the video input signal (e.g., NTSC video input signal) isconverted to a digital image. This digital image is processed by aseries of digital filters. The goal of these operations is to constructa processed video image that is to be presented to the retina by way ofelectrical stimulation. This includes any contrast, brightness or zoommanipulation as well as any additional filtering to convert the videoimage to the inferred “neural image” best suited for presentation to theretinal circuitry.

The goal of the video chain is to output an image that is to bepresented to the retina. This image to be presented to the retina shouldhave sufficient spatial resolution and a large enough field of view toaccommodate any spatial transformation needed to construct the emap (seebelow). The image to be presented to the retina should consist ofintensity values that are scaled from black (0) to white (255) in a waythat allows it to maximize the dynamic range for perceived brightnessgenerated by the emap (see below).

The Electrode Map (Emap)

The emap specifies the method for converting the output of the videochain to the temporal pattern of stimulation values for each electrodeand involves Spatial Mapping and Brightness Mapping.

The output of the video chain is an image that has higher resolutionthan the electrode array. The goal of the Spatial Mapping is todetermine which parts of the image are mapped to the individualelectrodes. The video image may be initially mapped to the electrodesusing the retinotopic co-ordinates (measured using fundus photograph) ofthe electrodes. A matrix transformation procedure may be used tosub-sample the image down to the resolution of the electrode array.These procedures will not be described here in detail because known perse to the person skilled in the art.

The above described basic retinotopic organization may be checked usingtwo-point discrimination. In particular, pairs of electrodes may bepresented in close temporal sequence and subjects may be asked about therelative position of the pair, e.g. did the dot pair move Left-Right orRight-Left. For example, subjects should be performing Up-Downdiscriminations for electrodes that are aligned horizontally inretinotopic co-ordinates.

Another method for determining the spatial mapping is to determine themap of the locations of the phosphenes generated by every electrode inthe array and use this map to determine which sections of the image eachelectrode is mapped to. The phosphene locations can be obtained bystimulating an electrode and asking the subject to place a reflectiveball in the 3D location of the phosphene. The 3D location of the ballcan be measured with an infrared stereo camera system. The advantage ofthis technique is that it directly takes into account any spatialdistortions in the perceived locations of the electrodes or phosphenes.The disadvantage is that it requires the experimenter to obtain a map ofthe phosphenes generated by every electrode. Interpolation techniquesmay be used to determine the spatial map of the phosphene locationswithout making a measurement for every electrode. If the mapping isorderly, it may be possible to sample fewer electrodes and still be ableto map the distortions in the perceived locations of the electrodes orphosphenes.

Once it has been determined which parts of the image are mapped to whichelectrode, a single number will be determined to represent thebrightness of that section of pixels in the image through BrightnessMapping. Various methods could be used to determine this value. Forinstance, the maximum value, the median value, the mean value, the mode,or the minimum may be used. This selection determines the singleintensity value that is to be transmitted to the retina, through anelectrical stimulation protocol.

The method of fitting Retinal Stimulation System 1 according to thepresent disclosure may include a technique for mapping the position inthe visual field of the phosphenes produced by stimulating eachelectrode in the electrode array 2 of FIG. 1. These phosphene locationsmay then be overlayed on the video image to determine the spatialregions of the video image that are mapped to each electrode. Forexample, in FIG. 45 one would expect that the regions of the human foveain the center part of the video image that are mapped to electrodes Band C to be smaller than the regions of the video image mapped toelectrodes E and F.

A block diagram of a visual prosthesis in the Retinal Stimulation System1 is shown in FIG. 46. The procedure for converting video camera inputto a pattern of electrical stimulation can be broken down into twogeneral parts: 1) the video chain and 2) the electrode map (EMAP).

The electrodes in the electrode array 2 of FIG. 1 of the visualprosthesis can be stimulated individually under computer control asshown in FIG. 47. This direct method of stimulating the electrodes isdistinct from video mode, where the video image determines thespatio-temporal pattern of electrode stimulation.

Each electrode in the electrode array 2 of FIG. 1 produces a phosphenewhen stimulated. Each electrode may be stimulated with the DirectStimulation Controller and the subjects will be instructed to trace theoutline of the phosphene on a board placed in front of them using ahandheld marker. A video splitter may be used to tap into the output ofthe video camera and the subject's indication of the phosphene locationis recorded with a Video Recorder. An automated image tracking programmay be used to find the coordinates of the marker, which gives a measureto the position of the phosphene in the video image.

The method according to the present disclosure provides a directmeasurement of the individual phosphene locations within the videoimage. Because the video image that is recorded is the same video signalthat serves as the input to the prosthesis during normal stand-alonesystem use, this allows a direct mapping between each electrode and thesection of the video image that should be map to this electrode.

FIGS. 48 and 49 show graphs of the phosphene locations recorded by thecamera and processed by the automated image processing program forstimulation of two different individual electrodes in a 16 electrodeepiretinal prosthesis. FIG. 50 shows the traced outline of the phospheneresulting from stimulation of all of the electrodes in the array. FIG.51 shows the perceived phosphene traced by the subject when a row andcolumn are stimulated together.

The results of these mappings may then be used to construct a lookuptable that specifies which sections of the video image are used todetermine the stimulation level sent to a given electrode. For instance,if a phosphene produces a large circle in the upper-left part of thevideo image, then the stimulation sent to this electrode is determinedby analyzing that part of the video image in real-time.

This method of mapping the video image to the spatial pattern ofstimulation accurately corrects any spatial distortions of theretinotopic map. It can rapidly and easily be done and results in aspatial map that is customized for each individual subject.

The goal of the Brightness Mapping procedure is to produce a perceptualbrightness level that corresponds to this intensity value. This can beaccomplished in a number of different ways. For instance, by varying thepulse amplitude to control brightness (amplitude coding), the pulsefrequency (frequency coding), the pulse width, or directly modulatingthe ganglion cell output with short electrical pulses of varyingfrequency (temporal coding). The emap needs to ensure that equallybright image values are transformed into stimulation patterns that giveas a result equally bright phosphenes. This mapping is established bydetermining the pulse parameter value to be mapped to the minimum imagevalue (0) for each electrode, determining the pulse parameter value tobe mapped for the maximum image value (255), and determining the mappingfor the intermediate values.

For amplitude coding, the 0 intensity value may be set to be equal tothe threshold pulse amplitude for every electrode. For the electrodewith the median threshold, the 255 intensity value may be set to themaximum safe current level. The more sensitive electrodes will have the255 intensity value mapped to the current amplitude that matches thebrightness of the median electrode at its maximum current level. Whenthe less sensitive electrodes are set to their maximum amplitude, theywill be perceptually dimmer than the median electrode at its maximumamplitude. Every electrode will linearly map the intensity values to theamplitude range between the specified min and max values. For the lesssensitive electrodes, the maximum intensity value that can be brightnessmapped to the median electrode, and all higher intensity values, will bemapped to the maximum amplitude.

Electrode interactions can be calculated by stimulating “clumps” ofmultiple electrodes (e.g., 2×2 or 4×4).

In FIG. 5, the brightness functions for individual electrodes are shownby dotted lines 300. The threshold may be considered as having abrightness of “1”. The subjects may be asked to rate the brightness forthe clump at maximum safety levels (again in comparison to the“standard” single electrode at the center of the array). See also S12 inFIG. 4. If the brightness doesn't sum across the electrodes, then thethreshold current level should be the minimum threshold current of thefour electrodes (the threshold for the most sensitive electrode) and thebrightness rating for the clump on max should be the mean brightnessrating of the clump of electrodes, as shown by the line 303 in FIG. 5.If the brightness sums across electrodes fully then the thresholdcurrent would be the sum of the currents (˜¼ the individual currents fora 2×2 clump) and the apparent brightness of the entire clump ofelectrodes would be the sum of the clump (˜4× the brightness of theindividual electrodes for a 2×2 clump), as shown by line 301 of FIG. 5.

It is likely that summation will be somewhere between the two extremes301 and 303, as shown by line 302 of FIG. 5. The summation can becalculated as brightness rating ofclump=(1−p)(aBnsBC+bBnsB)+p(aBpsBC+BpsB) where BBnsB=aBnsBC+bBnsB is thepredicted brightness rating equation for no summation, andBBpsB=aBpsBC+bBpsB is the predicted brightness rating equation forperfect summation. p is the amount of summation across electrodes—whenp=1 there is perfect summation, p=0 means there is no summation. If p issignificantly larger than 1 then the lookup tables may be based on theassumption that a certain number of electrodes will be stimulated at agiven time.

The subjects may be asked to rate the brightness of current amplitudeshalfway between threshold and max brightness level. If the linear modelis correct, the brightness rating value should be roughly midway betweenthe rating of the max brightness level and 1. If not, fit the data witha suitable nonlinear function such as a power function.

A check for spatial homogeneity may also be performed. In other words,it is checked whether neighboring electrodes do have similar brightnessfunctions for both threshold values, and for the brightness rating atmaximum safe charge density levels.

A summary of the procedure described above is shown in FIG. 6. A subjectis provided with a video camera associated with a pair of glasses (S14).An image is captured through the video camera (S15). The image is sentto a video processing unit VPU (S16) and converted to a digital image(S17). The digital image is processed (S18), its intensity values beingscaled from black to white (S19), and presented to the retina of thesubject or patient by way of electrical stimulation (S20). The aboveprocedure also determines which parts of the processed digital image aremapped to individual electrodes of the visual prosthesis (S21) anddetermines a map of location of phosphenes generated by each electrode(S22). This can be done either by a reflective ball placement (S23) orby means of interpolation techniques (S24).

Testing Methods to Confirm Fitting

In a typical eye exam, a simple stimulus (a letter) may be used and anoptometrist tries two lenses and asks us which one looks better. Theoptometrist uses this to gradually iterate to an optical prescription.This can be used to quickly determine whether a change in stimulusparameters (e.g. frequency) might possibly suit a patient better. Itwill also help to determine whether any changes in stimulation protocolor engineering design over time is really resulting in improvedperformance in patients. One possible fitting image might be of about 16electrodes simultaneously stimulated.

Spatial Resolution Test

Subjects have to decide whether the resulting rectangle is horizontallyor vertically oriented. The task can vary in spatial difficulty asfollows (from easy to hard); 8×2, 7×2, 7×3, 6×3, 5×3, 5×4.

Brightness Linearity Test

Brightness maps may be examined by varying the brightness of the squarecompared to the background and either asking subjects to rate theevenness of the square in terms of its brightness (implying that thebrightness across electrodes is well matched) or rate the brightness ofthe square (to measure whether the clumped estimated brightness maps aresuitably linearized).

After the implantation of the visual prosthesis in the subject, thefollowing examinations may be done on the subject with the device ON andOFF to provide control measures that can be used to optimize the device.

Electrode Impedance may be used to determine the electricalcharacteristics of the array interface with the retina. Using the“Measure Impedance” of the Fitting System described below, electrodeimpedances will be recorded on all electrodes via the VPU.

Electrode Threshold may be used to determine the minimum stimulationrequired to elicit a percept from one electrode. The stimulation may beperformed using single pulses, cathodic first, with all waveform phasesset to 0.45 ms using the Fitting and Psychophysical Test Systemsdisclosed below. The subject may control the amplitude of the test pulseand will manipulate it up and down until he/she has determined the levelat which a phosphene is just detected.

A First Stimulation Procedure may be used to expose the subject toelectrical stimulation using the Fitting System described below andrecord the subject's initial observations and responses. The followingmay be done to perform the test.

-   a. The external Fitting system may be configured for Communications    Mode. A separate Operating Room coil may be used if there is    residual swelling at the implant site which would make wearing the    Camera/Glasses uncomfortable or painful.-   b. An electrode impedance will be obtained.-   c. A single electrode will be selected for initial stimulation.-   d. The amplitude of stimulation will be increased and the subject    asked to describe any sensation. If a percept occurs, the subject    will be asked to describe it.-   e. Testing may be repeated on subsequent electrodes.-   f. At the discretion of the investigator, multiple electrodes may be    stimulated simultaneously using the procedure above.

A VisQOL (vision and quality of life) survey can be used to evaluate thevision related quality of life of the study subjects. The VisQOL HealthSurvey is a health-related quality of life instrument that has beenvalidated and used in low vision subjects. The use of this instrumentmay provide a baseline for the general quality of life for the subjectsand the impact of a retinal implant on their outlook. This instrumentwill be given to the subject pre-implant, then at prescribed intervalspost-operatively. Each question of the VisQOL survey may be read aloudto the subject and the response recorded. Results will be scoredaccording to the published methods for the survey.

A Massof Inventory may be used to evaluate the vision related activitiesof daily living of the study subjects. The Massof Inventory is a seriesof activity related questionnaires that allow discrimination of both theusefulness and the difficulty of each task. Through the evaluation oftasks the subject finds useful or pleasurable, the inventory provides ameasure of the “real-world” daily living changes, rather than artificialconstructs. This yields a meaningful measure without the risks of thesubject “training to the test.” Each question of the Massof Inventorymay be read aloud to the subject and the response recorded. Results willbe scored according to the published methods for the survey.

A Functional Assessment of Self Reliance on Tasks (FAST) may also beused to evaluate the vision related activities of daily living of thestudy subjects. The FAST instrument has been developed by the SouthernArizona VA Health Care System, Blind Rehabilitation Service for theevaluation of the progress of subjects with degenerating vision duringrehabilitation. In the instrument, clinical observers rate the subject'sability to perform simple daily living functions on a 1 to 10 scale.Each item of the FAST is evaluated by site staff trained in theinstrument. Each item on the instrument will be evaluated serially.Results will be scored according to the published methods for theinstrument.

A Psychophysical Test may be used to provide potential subjects with anexperience similar to post-operative psychophysical testing. Due to theintensive nature of the post-operative psychophysical testing, subjectsmay be tested using an auditory test. This test will not be used toevaluate hearing. Each potential subject may be provided headphonesconnected to a tone generator. A single tone of 0.5 seconds will bepresented. A second tone of a different loudness (with the samefrequency) will then be presented. The subject will be asked which tonethey perceived as louder. The test may be repeated twenty times.

Spatial Mapping of Phosphenes can be used to determine the relationshipbetween the physical positions of the individual electrodes on theretina and the perceived locations of the phosphenes induced in thesubject's visual field. Before every trial, the seated subject will beinstructed to place a magnetic token on a wall-mounted metal board inthe position felt to be “front and center”. This position will be takento be coordinate position (0, 0). A randomly chosen electrode may thenbe stimulated with a single 0.45 ms supra-threshold pulse and thesubject instructed to position a second magnetic token in the perceivedlocation of the phosphene. Each electrode may be stimulated twelvetimes. The average position of the phosphene corresponding to eachelectrode, relative to (0, 0), will be calculated. A calibrated,validated three-dimensional tracking system may also be used to capturespatial locations of phosphenes.

Brightness Matching may be used to determine the relationship betweenelectrode stimulation and percept brightness. Brightness matching may beperformed using the Fitting and Psychophysics Test Systems describedbelow. The subjects may be presented with a standard current of, forexample, 45 μA. The subjects may then be presented with pulses that varyin amplitude and will be asked to indicate which pulse was brighter.This procedure may be repeated multiple times across differentelectrodes to determine the relative current amplitude. From the dataobtained, the current amplitude required to elicit the same perceivedbrightness for each electrode may be determined.

Motion Discrimination may be used to test the ability of the subjects tocorrectly discriminate the direction of motion of a high contrast movingbar. The electrode amplitudes are set to 30 μA above the threshold foreach electrode. The stimulation will be set to a temporal frequency thatwas comfortable for each subject. For the experiments done with thecamera, the camera zoom will be set to provide a 1:1 matching of thevisual angle subtended by the array on the retina. The experimentalparadigm is a four alternative forced choice paradigm (4AltFC). For thefirst experiment, the electrodes on the array may be directly stimulatedby a bar (horizontal or vertical in shape; 10°×2.5°) moving in any oneof four cardinal directions (Test Pattern mode). The direction of motionof the bar may be varied randomly on a trial by trial basis. The speedof the moving bar may be varied from approximately 4°/s to 16°/s. Thesubject will be instructed to identify the direction of motion, and thenverbally indicate the direction to the observer. The trials may berepeated in blocks of 20.

For the second experiment, a similar high contrast bar (horizontal orvertical in shape; 10°×2.5°) may be projected onto a screen in front ofthe head-mounted camera of the subject, moving in any one of fourcardinal directions (Camera mode). The direction of motion of the barmay be varied randomly on a trial by trial basis. The speed of themoving bar may be varied from approximately 4°/s to 16°/s. The subjectwill be instructed to identify the direction of motion, and thenverbally indicate the direction to the observer. The trials may berepeated in blocks of 20.

Flicker Fusion may be used to determine the frequency at which repeatedstimuli merge. An electrode will be stimulated at different frequencies,with the same pulse parameters. The subject may be asked to report anyapparent flickering of the percept.

Orientation and Mobility Task may be used to evaluate the orientationand mobility of subjects. Geruschat, Turano et.al. have used a simplemobility task consisting of a corridor with high contrast obstacles toevaluate the orientation and mobility of low vision subjects. It wasfound that the time to traverse the course was correlated to visualacuity and field. This study will utilize a greatly simplified course.Each subject will be asked to follow a straight line and in a secondtest asked to find and touch a high-contrast target on the wall. Thesubject's time and accuracy will be evaluated. This instrument will begiven to the subject pre-implant, then at prescribed intervalspost-operatively. Each test may be performed with the implant ON andOFF. The subject may be instructed to walk each predefined course asquickly and safely as possible using any mobility aid. The distance thesubject is away from the target at the end of the task and the time totraverse the course will be noted. Each course may be tested three timeswith the implant OFF and then three times with the implant ON.

Each of the three runs may consist of a different starting position:

-   -   Straight ahead,    -   Turned approximately 10° right, and    -   Turned approximately 10° left.        The order of the starting positions may be randomly determined        by the observer.

Referring to FIG. 7, the subject may be placed 20 feet (6 meters) from awall with a contrasting 3′×7′ (1 m×2.1 m) rectangular target “door”. Thesubject will be asked to walk to the “door” and place a hand on the“door”. The distance the subject's hand is outside the “door” area(measured perpendicularly) and travel time will be recorded.

Referring to FIG. 8, the subject may be placed at the start of a line 20feet (6 meters) long which contrasts with the floor surface brightness.The subject will be asked to walk along the line. At the end of theline, the subject will be instructed to stop. The distance the subjectis away from the end of the line (measured perpendicularly from thenearest edge) and travel time will be recorded.

FIG. 9 shows a procedural flow during performance of the methodsdisclosed herein.

Referring to FIG. 10, a Fitting System (FS) according to the presentdisclosure may be used to configure and optimize the visual prosthesis 3of the Retinal Stimulation System 1.

The Fitting System may comprise custom software with a graphical userinterface running on a dedicated laptop computer 10. Within the FittingSystem are modules for performing diagnostic checks of the implant,loading and executing video configuration files, viewing electrodevoltage waveforms, and aiding in conducting psychophysical experiments.A video module can be used to download a video configuration file to aVideo Processing Unit (VPU) 20 and store it in non-volatile memory tocontrol various aspects of video configuration, e.g. the spatialrelationship between the video input and the electrodes. The softwarecan also load a previously used video configuration file from the VPU 20for adjustment.

The Fitting System can be connected to the Psychophysical Test System(PTS), located for example on a dedicated laptop 30, in order to runpsychophysical experiments. In psychophysics mode, the Fitting Systemenables individual electrode control, permitting clinicians to constructtest stimuli with control over current amplitude, pulse-width, andfrequency of the stimulation. In addition, the psychophysics moduleallows the clinician to record subject responses. The PTS may include acollection of standard psychophysics experiments developed using forexample MATLAB (MathWorks) software and other tools to allow theclinicians to develop customized psychophysics experiment scripts.

Any time stimulation is sent to the VPU 20, the stimulation parametersare checked to ensure that maximum charge per phase limits, chargebalance, and power limitations are met before the test stimuli are sentto the VPU 20 to make certain that stimulation is safe.

Using the psychophysics module, important perceptual parameters such asperceptual threshold, maximum comfort level, and spatial location ofpercepts may be reliably measured. Based on these perceptual parameters,the fitting software enables custom configuration of the transformationbetween video image and spatio-temporal electrode stimulation parametersin an effort to optimize the effectiveness of the retinal prosthesis foreach subject.

The Fitting System laptop 10 is connected to the VPU 20 using anoptically isolated serial connection adapter 40. Because it is opticallyisolated, the serial connection adapter 40 assures that no electricleakage current can flow from the Fitting System laptop 10.

As shown in FIG. 10, the following components may be used with theFitting System according to the present disclosure. A Video ProcessingUnit (VPU) 20 for the subject being tested, a Charged Battery 25 for VPU20, Glasses 5, a Fitting System (FS) Laptop 10, a Psychophysical TestSystem (PTS) Laptop 30, a PTS CD (not shown), a Communication Adapter(CA) 40, a USB Drive (Security) (not shown), a USB Drive (Transfer) (notshown), a USB Drive (Video Settings) (not shown), a Patient Input Device(RF Tablet) 50, a further Patient Input Device (Jog Dial) 55, GlassesCable 15, CA-VPU Cable 70, CFS-CA Cable 45, CFS-PTS Cable 46, Four (4)Port USB Hub 47, Mouse 60, LED Test Array 80, Archival USB Drive 49, anIsolation Transformer (not shown), adapter cables (not shown), and anExternal Monitor (not shown).

The external components of the Fitting System according to the presentdisclosure may be configured as follows. The battery 25 is connectedwith the VPU 20. The PTS Laptop 30 is connected to FS Laptop 10 usingthe CFS-PTS Cable 46. The PTS Laptop 30 and FS Laptop 10 are pluggedinto the Isolation Transformer (not shown) using the Adapter Cables (notshown). The Isolation Transformer is plugged into the wall outlet. Thefour (4) Port USB Hub 47 is connected to the FS laptop 10 at the USBport. The mouse 60 and the two Patient Input Devices 50 and 55 areconnected to four (4) Port USB Hubs 47. The FS laptop 10 is connected tothe Communication Adapter (CA) 40 using the CFS-CA Cable 45. The CA 40is connected to the VPU 20 using the CA-VPU Cable 70. The Glasses 5 areconnected to the VPU 20 using the Glasses Cable 15.

The graphical user interface of the Fitting System may have six optionson the FS Main Menu 7 as shown in FIG. 11. For example, Subject Testing,Transfer Session, Archive Sessions, Load Security File, Maintenance, andExit.

The Subject Testing option may be selected when performing: diagnosticcheck (i.e. impedance and waveforms) on the status of the implant,viewing waveforms for selected electrodes, loading a video configurationfile to the VPU and stimulating the subject using the downloaded videostimulation parameters, executing psychophysical experiments. TheTransfer Session option may be selected when copying file(s) to a thumbdrive. The Archive Sessions option may be selected when archiving alldata files on the FS laptop 10 to the external drive 49. The LoadSecurity File option may be selected to enable use of the FittingSystem. The Load Security File option may be chosen at the initialclinical testing session. The Maintenance option may be selected toperform maintenance on one or more components of the system. TheMaintenance option may be set up to only be accessed by an authorizedperson. The Exit option may be selected to close out the main menu.

The Subject Testing option is more fully described in the followingparagraphs.

Prior to using a VPU 20 with a new subject for the first time, thefollowing steps may be performed by an authorized person to configurethe VPU 20: 1) Confirm that the VPU 20 is configured for use, 2) Matchthe VPU 20 to an implant, 3) Program the VPU 20 with the Subject's ID,and 4) Label the VPU 20 with the Subject's ID.

Prior using the Subject Testing option, the VPU 20 should be on, thesubject should put on the Glasses 5, the Glasses 5 should be adjusteduntil a link is obtained with the implant, and the VPU 20 should confirmthat the implant is working by running start-up tests.

Once the Subject Testing option is selected from window 7, a loginscreen 8 shown in FIG. 12 may be displayed with fields for User ID,Password and Subject ID.

After the login, a diagnostic application may be initiated to displaythe status of the implant. Through the diagnostic application, anelectrode integrity check may be performed and the electrode status maybe displayed and the impedance and waveforms for each of the electrodescan be measured.

An “Electrode Integrity” message box 6, shown in FIG. 13, may bedisplayed in the event that any newly broken/shorted electrodes aredetected or broken/shorted electrodes are present. If no newly detectedbroken/shorted electrodes are detected, this message box will not appearand the diagnostics screen 109 shown in FIG. 14 may be displayed.

The Diagnostic Module Screen 109 shown in FIG. 14 may contain: 1)Session Information 101 displaying (a) Experimenter (User) ID, (b)Subject ID, (c) VPU Connection identifying the status of the connectionof the VPU to the FS, (d) Implant Connection identifying the status ofthe connection of the implant to the FS, and (e) Stimulation identifyingthe status of stimulation (i.e., whether or not stimulation isoccurring); 2) Measure Impedance 103 for measuring impedance for theelectrodes; 3) Measure All Waveforms 104 for measuring waveforms for theelectrodes; 4) Broken Electrodes/Impedance (in kOhms)—6×10 ElectrodeGrid 105 representing each of the implant electrodes. The view of theelectrodes is from the perspective of the subject. The electrodes shownas “{circle around (x)}” are designated as broken/shorted. Whenmeasuring impedance, the values will appear directly under eachrepresented electrode. Stimulation should not occur on electrodesdesignated as broken; and 5) Impedance Scale 102 for impedance thatranges from 0 to 45 kOhms.

Clicking on the Measure Impedance 103 will measure impedance of theelectrodes and a message box shown in FIG. 15 may be used to indicatethe progress of obtaining impedance measurements. Once the impedancemeasurements are completed, the impedance values (in kOhms) will bedisplayed as shown in FIG. 16 under each represented electrode. Each ofthe electrodes may be color coded based on where the impedance valuefalls within the impedance scale from 0 to 45 kOhms of the ImpedanceScale 102. The impedance values for the subject may be automaticallystored in a file marked for transfer on the FS laptop 10.

To measure waveforms, Clicking on “Measure All Waveforms” 104 willmeasure waveforms of the electrodes and a message box shown in FIG. 17may be used to indicate the progress of the waveform measurements. Oncethe measurements are complete, the waveform information may be stored ina file marked for transfer on the FS laptop 10. The waveforms for eachof the electrodes can be viewed from the Waveform Viewer 107.

The Waveform Viewer 107 shown in FIG. 18 is a utility that may be usedto measure and view the waveform of a selected electrode. From the listof the electrodes at the bottom of the screen (displayed in a 6×10configuration 110 with their Cartesian coordinates), a specificelectrode for which to measure the waveform may be selected. Uponselection of the electrode, the VPU 20 will record the waveform and theinformation will be sent to the FS so that the waveform data may bepresented on the screen as shown in FIG. 19 in which, for example, thewaveform of A03 is measured during stimulation. By right clicking on themouse, it may be possible to zoom in and zoom out on the displayedwaveform. The waveform may be saved by clicking on the Save Waveformbutton 111.

The video application 108 may be used to load a video configuration fileto the VPU 20 to allow the VPU 20 to be used properly in Stand-Alonemode. The video configuration file provides the instructions for thestimulation that each electrode will deliver based on the video streamcaptured by a camera located on the Glasses 5.

The video configuration files may be in a comma separate value (.csv)format. The video configuration file may define the following: 1)Comment: Begin a line with “#,” to insert a comment on any line. Theselines will be displayed in the message window in the video module of CFSwhen a particular video configuration file is loaded, 2) Templateformat: The VPU 20 and FS accommodates certain formats for a videoconfiguration file. The format used must be specified in the file, 3)Current amplitude range: Specify the current amplitude range (one valuefor all electrodes), 4) Stimulation frequency: Specify the frequency atwhich stimulation will occur (one value for all electrodes), 5) Pulsetiming profile specification: Six pulse timing profiles should bespecified. These six profiles form a library from which individualprofiles can be chosen for creating the anodic and cathodic pulses foreach electrode, 6) Brightness map: Specify the brightness map for eachelectrode, 7) Cathodic and anodic profiles for each electrode: From thelibrary of pulse timing profiles, specify a timing profile for thecathodic and anodic pulses for each electrode, and 8) Spatial map:Specify the spatial map for each electrode (x, y coordinates). Multiplevideo configuration files may be created for each subject.

The Video 108 may consist of three sub-sections as shown in FIG. 20.They may be a ‘Stimulation’ section 112, a ‘Configure Video’ section113, and a ‘Current Configuration’ section 114. Within the ‘Stimulation’section 112 is the button to start stimulation of the subject with thevideo configuration file downloaded to the VPU 20. The ‘Configure Video’section 113 has two buttons: “Load Configuration to VPU” and “Revert tomost recently used configuration.” The “Load Configuration to VPU” maybe used to load the desired video configuration file to the VPU 20. The“Revert to most recently used configuration” may be used to bring up thevideo configuration file that was last used for stimulation. The‘Current Configuration’ section 114 may be used to display the residentvideo configuration on the VPU 20 by providing the file name, the dateit was loaded, and a description of the file (if applicable).

To load a different video configuration file to the VPU 20, one may usethat “Load configuration to the VPU” option to bring up a ‘Load’ screenshown in FIG. 21 to show a listing of video configuration files.Clicking on a configuration file in FIG. 21 will display a descriptionof that selected file in the description box provided that thedescription was included as part of the video configuration file. Whenthe desired video configuration is located, a “Load Selection” option inFIG. 21 may be used to load file to the VPU 20. The file name, alongwith the load date and time will be displayed in the “Currentconfiguration” section 114 on the Video Screen in FIG. 20. The VPU 20may be set up to not download any file that does not meet the necessarysafety requirements for stimulation.

Once a desired video configuration file is loaded, a stimulation of thesubject may be performed using START STIMULATION in section 112 of FIG.20. A stimulation window shown in FIG. 22 may be used to display apixelized representation in a 6×10 grid of the filtered image displayedto the subject. A 12×20 pixelized image, which is twice the resolutionof the filtered image, can also be displayed.

The Psychophysical Test System (PTS) is part of the Retinal StimulationSystem 1 as it is intended to be used to facilitate fitting a subject bycharacterizing the subject's perceptual responses to electrical stimuli.The results from the psychophysical experiments may be accumulated,evaluated and used to determine the stimulation parameters of the VPU 20during video stimulation.

Additionally, PTS may provide a framework for researchers andinvestigators to develop customized psychophysical experiments. PTS maycomprise four ways to execute psychophysical experiments: 1) Thresholdwith Method of Adjustment, 2) Brightness Matching, 3) DirectStimulation, and 4) Clinician-Designed Research Experiments. Each beingdescribed in detail below.

The Threshold with Method of Adjustment may be used to determine thestimulation current threshold for an individual electrode (i.e. thestimulation level at which a percept is first seen). The user interfaceallows the experimenter to (1) configure the experiment, including whichelectrodes to test, how many trials are tested per electrode and otherstimulation timing parameters, (2) preview the stimulation waveform, (3)capture subject responses, and (4) view experiment results on the screenas the test progresses, and save the results.

In this test, the subject will be stimulated on one of the testelectrodes. The subject may use the Patient Input Device (Jog Dial) 55to increase or decrease the stimulation current amplitude on theselected electrode after each stimulation. To indicate the threshold,the subject may press down the Jog Dial 55 when perception occurs. TheResults screen displays the threshold and another test electrode istested. This continues until all selected electrodes are tested for anumber of trials, as configured by the experimenter. All stimulationparameters may be recorded by the Fitting System in the psychophysicslog.

The Brightness matching may be used to determine the relationshipbetween electrode stimulation current and the perceived brightness.These data are analyzed to determine the current amplitudes required toelicit the same perceived brightness for each electrode in the array.The user interface allows the experimenter to (1) configure theexperiment, including which electrodes to test, which electrode and whatamplitude to use as a reference, how long to wait between the twostimuli, the number of trials per test electrode, and other stimulationtiming parameters, (2) preview the stimulation waveform, and (3) viewthe stimulation and subject response as the test progresses.

In each trial, the subject may be stimulated with two stimuli, one onthe test electrode and one on the reference electrode (The order of thestimuli is random). The subject may use the keys on the Patient InputDevice (Tablet) 50 to signal which of the two temporal intervalscontains the brighter stimulus. This process will continue until each ofthe selected electrodes has been tested for a number of trials, asconfigured by the experimenter.

Using Direct Stimulation, an experimenter is able to (1) design astimulation wave form on a single or multiple electrodes and (2) conductmanual testing on a single or multiple electrodes. During the use ofDirect Stimulation, no subject response is automatically logged in FS.

The PTS System, may, for example, also have MATLAB software installed toallow clinicians to develop their own customized psychophysicalexperiments for research purposes. These experiments may be used forresearch purposes.

The following provides instructions for running the Threshold Method ofAdjustment, Brightness Matching, and Direct Stimulation Psychophysicalexperiments. By selecting the Psychophysics tab 106 of FIG. 14, FS willattempt to connect with PTS. “WAITING FOR CONNECTION,” as shown in FIG.23 may be displayed indicating that FS is waiting for a connection withPTS.

A window 129 shown in FIG. 24 will appear on the PTS laptop 30requesting Username 130, Password 131, and Subject ID 132 and the sitespecific Research Center ID 133. ‘OK’ 134 may be used to proceed to thePsychophysical Test System Main Menu and ‘Cancel’ 135 may be used toquit the session.

If ‘OK’ 134 is selected, the PTS Server screen on the FS Laptop 10should display “CONNECTED”, as shown in FIG. 25, to indicate that aconnection has been successfully established between the FS and PTS.

The Psychophysical Test System (PTS) main screen 139, shown in FIG. 26,has four options 1) ‘Threshold with method of adjustment’ 140, 2)‘Brightness matching’ 141, 3) ‘Direct Stimulation’ 142, and 4) ‘Quit’143.

Next, a way of conducting a threshold measurement using the method ofadjustment will be described.

A ‘Threshold with Method of Adjustment’ screen 144 shown in FIG. 27appears when the ‘Threshold Method of Adjustment’ button 140 is selectedfrom the ‘PTS Main Menu’ screen 139. The ‘Threshold with Method ofAdjustment’ screen 144 may contain:

1) a ‘Parameters’ panel 150 for experiment parameters that requireconfiguration in order to execute an experiment,

2) a ‘Stimulation’ panel 151 for stimulation parameters that requireconfiguration in order to execute an experiment;

3) a ‘Message’ panel 152 for messages that may require theexperimenter's attention during the testing. There are two types ofmessages than can be displayed during a test session: (a) Unknown keypressed—This message is generated if the subject presses an unknown keyduring the test, and (b) Maximum or minimum amplitude reached—Thismessage is generated if the maximum/minimum current amplitude is reached(as allowed by the maximum charge per phase safety limit) and thesubject continues to turn the jog dial to increase/decrease theamplitude. A loud sound may also be emitted to alert the experimenterand the subject;

4) a ‘Result’ panel 153 for displaying electrodes that are currentlyunder test, stimulation amplitude and previously recorded thresholds inthis experiment;

5) a ‘Run’ button 154 to start to run the threshold with method ofadjustment experiment. The program will check the parameters enteredagainst the safety limits and the experimenter will have a chance tocorrect them if so;

6) a ‘Cancel’ button 155 to cancel the current running experiment; and

7) an ‘Invalidate Last Trial’ button 156 to invalidate the last foundthreshold if the subject pushed the jog dial by accident.

Configuration parameters may be entered for the experiment as describedbelow with reference to FIG. 27.

The names of electrode(s) whose thresholds are to be measured duringtesting may be entered in the ‘Electrode Name’ window 160 of the‘Parameters’ panel 150. One may select all the electrodes by selectingthe ‘All Available Electrodes’ window 162 of the ‘Parameters’ panel 150or one may select only certain electrodes from the grid shown in a Table1 below.

TABLE 1 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 C1C2 C3 C4 C5 C6 C7 C8 C9 C10 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 E1 E2 E3 E4E5 E6 E7 E8 E9 E10 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10The starting stimulation amplitude(s) (μA) for each of the testelectrodes may be entered in the ‘Start Amplitude’ window 161 of the‘Parameters’ panel 150. A ‘Unified Start Amplitude’ window 163 of the‘Parameters’ panel 150 may be checked to enter a single Start Amplitudefor all electrodes.

The number of threshold measurements to be made on each electrode may beentered in the ‘Trials per electrode’ window 164 of the ‘Parameters’panel 150.

The pulse Width (ms) may be entered into windows 165 a-d of the‘Stimulation’ panel 151. The desired time between start of the effectivestimulation window and initiation of the first phase may be entered intoa Tw window 165 a. The duration of the first phase may be entered into aTx window 165 b. The desired time between the end of the first phase andthe beginning of the second phase may be entered into a Ty window 165 c.The duration of the second phase may be entered into a Tz window 165 d.FIG. 28 depicts a waveform of the numbers entered into windows 165 a-d.

The frequency of how many times per second the waveform shown in FIG. 28will be repeated may be entered into a ‘Frequency’ window 166 of the‘Stimulation’ panel 151. The desired length of each stimulation inmilliseconds (i.e. the length of stimulation at a given test amplitude)may be entered into a ‘Duration’ window 167 of the ‘Stimulation’ panel151. Selection of whether the first phase is negative (cathodic) orpositive (anodic) current may be performed using ‘First’ window 168 ofthe ‘Stimulation’ panel 151. A ‘Show waveform’ button 169 may be used toproduce a graph that plots the waveform of the complete stimulus for atrial. A ‘Sound w/o stimulation’ button 170 may be used to generate asound (the same as the one heard when stimulation is delivered) withoutactually delivering stimulation. Once all configuration parameters havebeen entered, the experimenter has the option to press the ‘ShowWaveform’ button 169 prior to initiating the experiment to check theparameters to produce a graph that plots the waveform of the completestimulus for a trial as shown in FIG. 29. A ‘Run’ button 154 may be usedto proceed with the experiment.

After the ‘Run’ button 154 or ‘Show Waveform’ button 169 are activated,the parameters may be checked against safety requirements of the system.If any of the parameters violates safety limits, a message box may bedisplayed and the experimenter will need to change the configurationparameters. Common errors may include broken/shorted electrodes andstart amplitudes which exceed maximum charge per phase limit. Forexample, if any of the chosen electrodes are already deemedbroken/shorted, a popup message shown in FIG. 30 may be displayed on thescreen. If no safety violations are found, a popup message shown in FIG.31 will appear. If the requested pulse amplitude cannot be generated bythe VPU 20, the closest value will automatically be used. The value willappear in the results section discussed below.

After each stimulus presentation, the subject may turn the jog dial 55to the right to increase stimulation amplitude, or may turn the jog dial55 to the left to decrease stimulation amplitude. The subject mayincrease or decrease the stimulation level until he/she has determinedtheir threshold (i.e. the minimum stimulation amplitude for seeing thestimulation.) The subject may signal the threshold for that electrode bypressing down on the Jog Dial 55. If multiple electrodes are tested, theelectrodes may be tested in random order.

During a Threshold with Method of Adjustment experiment, the PTS Serverscreen on the FS Laptop 10 may display ‘RUNNING: Threshold with methodof adjustment’ is shown in FIG. 32. At any time during the experiment,the experimenter can click the ‘Sound w/o stimulation’ button 170 togenerate a stimulation sound without actually delivering stimulation tothe subject.

If for any reason, the experimenter determines that the last thresholdmeasurement is invalid (e.g. the subject pressed down the jog dial 55accidentally), the experimenter can click on the ‘Invalidate Last Trial’button 156 to invalidate that trial. This may be set up to invalidateonly the results of the last trial, not the whole experiment. The‘Result’ panel 153 will show the trial as “Invalid” and the trial willbe repeated in a random order with the remaining electrodes as shown inFIG. 29.

The experiment ends once all of the trials have been completed. In the‘Result’ panel 153, the total number of trials and number of finishedtrials may be displayed throughout the experiment. The ‘Cancel’ button155 may be used to stop an experiment prior to the completion of alltrials.

At the end of the experiment, the “Threshold with method ofadjustment—results” screen shown in FIG. 33 may appear and theexperimenter may have the option of saving the results to a hard drive.

After saving the results and/or canceling, a ‘Comment’ screen 175 shownin FIG. 34 may be used for comments. The ‘Comment’ screen 175 containstwo buttons, ‘Repeat Last Experiment’ 176 and ‘Go Back to Main Menu’177. If ‘Repeat Last Experiment’ 176 is chosen, the experimenter will bereturned to the main Threshold Test—‘Method of Adjustment’ screen 144 ofFIG. 27 with the Parameters from the last experiment and theexperimenter can modify and repeat the experiment. If ‘Go Back to MainMenu’ 177, is chosen, the experimenter will be returned to the main PTSmenu 139.

A ‘Brightness Matching’ screen 178 shown in FIG. 35 appears when the‘Brightness Matching’ 141 button is selected from the ‘PTS Main Menu’Screen 139. The ‘Brightness Matching’ screen 178 may contain 1)‘Parameters’ panel 180, 2) ‘Stimulation’ panel 181, 3) ‘Message’ panel182, and 4) ‘Result’ panel 183. During a Brightness Matching experiment,the PTS Server screen on the FS Laptop 10 may display “EXPERIMENT:Brightness matching” as shown in FIG. 36.

Configuration parameters may be entered for the experiment as describedbelow with reference to FIG. 35.

The name of the standard electrode that will be matched to thebrightness of each test electrode may be entered into the ‘ReferenceElectrode’ window 184 of the ‘Parameters’ panel 180. The electrodes maybe selected from the grid shown in Table 1 above.

The desired amplitude of the reference electrode that will be matchedmay be entered into the ‘Reference Amplitude’ window 185 of the‘Parameters’ panel 180.

The desired electrode(s) whose brightness is being varied to match thebrightness of the reference electrode may be identified in the ‘TestElectrode’ window 186 of the ‘Parameters’ panel 180.

The starting stimulation amplitude (μA) for each of the test electrodesmay be entered into the ‘Start Amplitude’ window 187 of the ‘Parameters’panel 180.

The number of brightness matching trials for each electrode may beentered into ‘Trials per electrode’ window 188 of the ‘Parameters’ panel180.

The desired time delay between the reference and test stimuli may beentered into the ‘Time between Stimulation’ window 189 of the‘Parameters’ panel 180.

The Pulse Width (ms) may be entered into windows 190 a-d of the‘Stimulation’ panel 181. The desired time between start of the effectivestimulation window and initiation of the first phase may be entered intothe Tw window 190 a. The duration of the first phase may be entered intoa Tx window 190 b. The desired time between the end of the first phaseand the beginning of the second phase may be entered into a Ty window190 c. The duration of the second phase may be entered into a Tz window190 d. FIG. 28 depicts a possible waveform of the numbers entered intowindows 190 a-d.

The frequency of how many times per second the waveform shown in FIG. 28will be repeated may be entered into a ‘Frequency’ window 191 of the‘Stimulation’ panel 181. The desired length of each stimulation inmilliseconds (i.e. the length of stimulation at a given test amplitude)may be entered into a ‘Duration’ window 192 of the ‘Stimulation’ panel181. Selection of whether the first phase is a negative (cathodic)current phase or a positive (anodic) current phase may be performedusing a ‘First’ window 193 of the ‘Stimulation’ panel 181. A ‘ShowWaveform’ button 194 may be used to produce a graph that plots thewaveform of the complete stimulus for a trial. A ‘Run’ button 195 may beused to proceed with the experiment.

After the ‘Run’ button 195 or ‘Show Waveform’ button 194 are activated,the parameters may be checked against safety requirements of the system.If any of the parameters violates safety limits, a message box may bedisplayed and the experimenter will need to change the configurationparameters. Common errors may include broken/shorted electrodes andstart amplitudes which exceed maximum charge per phase limit. Forexample, if there are any broken electrodes, the popup message shown inFIG. 37 may be displayed on the screen. If no safety violations arefound once the broken electrodes have been removed or if no brokenelectrodes are found, the popup screen shown in FIG. 38 will appearafter pressing ‘Run’ 195. If the requested pulse amplitude cannot begenerated by the VPU 20, the closest value will automatically be used.The value will be displayed in the results section.

In this experiment, the subject is stimulated with two stimuli, one onthe test electrode and one on the reference electrode. The order of thestimuli may be random. The subject may use the Tablet Patient InputDevice 50 and presses the tablet keys to indicate which of the twointervals contains the brighter stimulus. The ‘Results’ panel 183 shownin FIG. 39 displays the amplitude values of the reference and testelectrode for each trial. The program indicates which stimulus thesubject selected by enclosing it in parentheses. If the subjectindicates that the test electrode is brighter than the referenceelectrode, the system will decrease the test electrode amplitude and ifthe subject indicates that the standard (reference) electrode isbrighter, the system will increase the test electrode amplitude. Thepresentation of the reference and test electrodes may occur in randomorder on a trial-by-trial basis.

The experiment ends once all of the trials have been completed. TheResult panel 183 displays the total number of trials and the number offinished trials throughout the experiment. A ‘Cancel’ button 201 may beused to stop an experiment prior to the completion of all the trials.

At the end of the experiment, the ‘Comments’ screen 202 shown in FIG. 40may be used to allow the experimenter the option to comment. The‘Comments’ screen 202 contains two buttons, ‘Repeat Last Experiment’ 203and ‘Go Back to Main Menu’ 204. If ‘Repeat Last Experiment’ 203 ischosen, the experimenter will be returned to the main ‘BrightnessMatching’ screen 178 of FIG. 35 with the Parameters from the lastexperiment and the experimenter can modify and repeat the experiment. IfGo Back to Main Menu 204, is chosen, the experimenter will be returnedto the main PTS menu 139 of FIG. 26.

A ‘Direct Stimulation’ screen 210 shown in FIG. 41 appears when the‘Direct Stimulation’ button 142 of FIG. 26 is selected from the PTS MainMenu Screen 139 of FIG. 26. The ‘Direct Stimulation’ screen 210 may alsocontain 1) ‘Parameters’ panel 211, 2) ‘Stimulation’ panel 212, 3)‘Message’ panel 213, and 4) ‘Result’ panel 214. During a DirectStimulation experiment, the PTS Server screen on the FS Laptop 10 maydisplay “RUNNING: Direct Stimulation” as shown in FIG. 42.

Configuration parameters may be entered for the experiment as describedbelow with reference to FIG. 41.

Starting stimulation amplitude(s) (μA) for each of the selectedelectrodes may be entered into a ‘Start Amplitude’ window 220 of the‘Parameters’ panel 211. ‘Rastering’ 221 may be used to stagger the starttimes that electrodes are stimulated. When this option is not selected,all electrodes are stimulated simultaneously.

The number of times a stimulation will be repeated may be entered into a‘Repeat Stimulation’ window 222 of the ‘Parameters’ panel 211. The timedelay between successive repetitions may be approximately 0.5 seconds.

The electrodes to be stimulated can be selected from the ‘Electrodes’windows 223 of the ‘Parameters’ panel 211. The electrodes may beindividually selected by clicking individual boxes. Complete rows ofelectrodes may be selected or de-selected by clicking on the alphabeticbutton (A-F). Complete columns of electrodes may be selected orde-selected by clicking on the numeric button (01-10). All electrodescan be selected by using the ‘Set/Clear’ button 224. The inverse of theselected electrodes can be achieved by clicking on the ‘Inverse’ button225.

A Pulse Width (ms) may be entered into windows 226 a-d of the‘Stimulation’ panel 212. A desired time between start of the effectivestimulation window and initiation of the first phase may be entered intoa Tw window 226 a. The duration of the first phase may be entered into aTx window 226 b. The desired time between the end of the first phase andthe beginning of the second phase may be entered into a Ty window 226 c.Duration of the second phase may be entered into a Tz window 226 d. FIG.28 depicts a possible waveform of the numbers entered into windows 226a-d.

The frequency of how many times per second the waveform shown in FIG. 28will be repeated may be entered into a ‘Frequency’ window 228 of the‘Stimulation’ panel 212. A desired length of each stimulation inmilliseconds (i.e. the length of stimulation at a given test amplitude)may be entered into a ‘Duration’ window 229 of the ‘Stimulation’ panel212. Selection of whether the first phase is a negative (cathodic)current phase or a positive (anodic) current phase may be performedusing the first window 227 of the ‘Stimulation’ panel 212. The ‘ShowWaveform’ button 230 may be used to produce a graph that plots thewaveform of the complete stimulus for a trial. The ‘Run’ button 215 maybe used to proceed with the experiment.

After the ‘Run’ button 215 or ‘Show Waveform’ button 230 are activated,the parameters may be checked against safety requirements of the system.If any of the parameters violates safety limits, a message box will bedisplayed and the experimenter will need to change the configurationparameters. Common errors may include broken/shorted electrodes, startamplitudes which exceed a maximum charge per phase limit (or the maximumtotal instantaneous current limit). For example, if there are any brokenelectrodes, the popup message shown in FIG. 43 may be displayed on thescreen. While the experiment is running, the ‘Result’ screen 214 of FIG.41 will indicate that stimulation is in progress. The ‘Cancel’ button216 of FIG. 41 may be used to cancel Stimulation. A message (not shown)may appear indicating that stimulation was stopped by request.

If stimulation has ended normally, a Comment screen 236 shown in FIG. 44may be displayed. The Comment screen 236 contains two buttons, ‘RepeatLast Experiment’ 237 and ‘Go Back to Main Menu’ 238. If Repeat LastExperiment 237 is chosen, the experimenter will be returned to the mainDirect Stimulation screen 210 with the Parameters from the lastexperiment and the experimenter can modify and repeat the experiment. If‘Go Back to Main Menu’ 238, is chosen, the experimenter will be returnedto the main PTS menu 139.

A Clinician-Designed Research Experiments module allows researchers todevelop and execute their own custom-designed experiments for researchpurposes. Experimental psychophysical scripts are developed in MATLABand are then executed within a MATLAB/PTS framework.

Accordingly, what has been shown is an improved method of stimulatingneural tissue for improved response to brightness. While the inventionhas been described by means of specific embodiments and applicationsthereof, it is understood that numerous modifications and variationscould be made thereto by those skilled in the art without departing fromthe spirit and scope of the invention. It is therefore to be understoodthat within the scope of the claims, the invention may be practicedotherwise than as specifically described herein.

1. A method for fitting a visual prosthesis having a plurality ofelectrodes, the method comprising: selecting one electrode from among afirst electrode and subsequent electrodes as a standard electrode;determining a first perceived brightness level on the standard electrodeby patient feed back, wherein the first perceived brightness level onthe standard electrode is elicited by a first stimulation amplitude;approximating the first perceived brightness level on a second electrodeby setting a second stimulation level to be applied to the secondelectrode to the first stimulation amplitude applied on the standardelectrode; refining the second stimulation amplitude on the secondelectrode using further patient feedback to elicit the first perceivedbrightness level on the second electrode; and creating and storing a mapof brightness to electrode stimulation amplitudes based on theestablished stimulation amplitudes for the standard electrode and thesecond electrode, wherein the first and second stimulation amplitudesare provided by a stimulation system.
 2. The method of claim 1, furthercomprising: determining a second perceived brightness level on thestandard electrode by patient feedback, wherein the second perceivedbrightness level on the standard electrode is elicited by a thirdstimulation amplitude; approximating the second perceived brightnesslevel on the second electrode by setting a fourth stimulation amplitudeto be applied to the second electrode to the third stimulation amplitudeapplied on the standard electrode; and refining the fourth stimulationamplitude on the second electrode using further patient feedback toelicit the second perceived brightness level on the second electrode,wherein the third and fourth stimulation amplitudes are provided by thestimulation system.
 3. The method of claim 1, wherein the firstperceived brightness level on the standard electrode and the firstperceived brightness level on the second electrode are threshold levels.4. The method of claim 2, wherein the second perceived brightness levelon the standard electrode and the second perceived brightness level onthe second electrode are maximum levels.
 5. The method of claim 4,wherein the maximum level is a level of three quarters of a safetylimit.
 6. The method of claim 4, wherein the maximum level is a maximumcomfort level for the patient.
 7. The method of claim 2, wherein thefirst perceived brightness level on the first electrode and subsequentelectrodes is determined through a 150-750 ms train of 10-100 Hz pulses.8. The method of claim 1, wherein the standard electrode is theelectrode having a median threshold value.
 9. The method of claim 1,wherein the patient is subjected to a brightness comparison between thestandard electrode and each electrode different from the standardelectrode.
 10. The method of claim 1, wherein the patient is subjectedto a brightness comparison by rating brightness of a clump ofelectrodes.
 11. The method of claim 4, wherein the maximum level on thefirst electrode and subsequent electrodes is determined by graduallyincreasing an amplitude of stimulation pulses.
 12. The method of claim4, wherein determination of threshold and maximum levels on theelectrodes is performed by converting a video camera input to a patternof electrical stimulation.
 13. The method of claim 1, wherein therefining the second stimulation amplitude comprises: decreasing thesecond stimulation amplitude on the second electrode if perceivedbrightness of the second electrode based on patient feedback is brighterthan the first perceived brightness level on the standard electrode; andincreasing the second stimulation amplitude on the second electrode ifthe first perceived brightness level on the standard electrode isbrighter than perceived brightness of the second electrode based onpatient feedback, wherein the decreasing and the increasing is performedby the stimulation system.
 14. The method of claim 1, furthercomprising, for each particular electrode in the plurality of electrodesaside from the standard electrode and the second electrode:approximating the first perceived brightness level on a particularelectrode by setting an electrode stimulation amplitude to be applied toa particular electrode to the first stimulation amplitude applied on thestandard electrode; refining the electrode stimulation amplitude on theparticular electrode using further patient feedback to elicit the firstperceived brightness level on the particular electrode; and creating andstoring a map of brightness to electrode stimulation amplitudes based onthe established stimulation amplitudes for each electrode, wherein theelectrode stimulation amplitude is provided by the stimulation system.15. The method of claim 1, wherein the refining the second stimulationamplitude comprises adjusting at least one of pulse width, duration of acathodic phase, duration of an anodic phase, and duration between an endof either the cathodic phase or the anodic phase and a beginning of theother phase, wherein the adjusting is performed by the stimulationsystem.
 16. The method of claim 1, wherein the standard electrode is anelectrode having a maximum comfort level for the patient that is above asafety limit of the electrode.